Need advice from BHK Preamp owners

I have a DSD DAC feeding a BHK preamp then to a BHK 250 amp and out to my Focal 1038be speakers. Today, after no change to the system, the audio started sounding thin and bright.

I have a backup office system. On a hunch, I swapped out the BHK Preamp for my Schitt Freya S preamp. The thinness and brightness were gone. I repeated the swap two more times with the same results.

It seems the problem is isolated to the BHK preamp. The easiest thing to do that would not require sending it in for repairs is to swap tubes. They have about 1,500 hours on them. What I don’t know is if thinness and brightness are a symptom when these tubes go south.

Have any of you had a similar experience that was cured by new tubes?


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Replace your tubes.

When tubes age, they degrade gradually until they lose detail. Did this happen just today, and to both channels at the same time?
I use nothing but these tubes:
Genalex Gold Lion Pair 12AU7 |
$70.49 a matched pair.

When tubes wear out they sound “muddy.” Detail is fuzzy and it’s just a bit off.

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No hum/grounding problem or so? I don’t think degraded tubes do this.


Just try new tubes. In the meantime, you can also use the volume control in the DAC, using it as your preamp.

Agree with all who recommend replacing the tubes. I wish we could get the “tube sound” without the nearly organic vacuum tubes in the chain.

I don’t agree that there is one definable “tube sound”. And I have and love tubes for lots of reasons, not all for the sound.
But may I answer your thought with: Pass Labs.


Thank you. Even though the system suddenly sounding thin and bright is not a symptom other users may have experienced, it does not hurt to have a backup pair of tubes to swap in and help diagnose. PS Audio sells them for $100 and someone suggested another source.

Are you sure the system changed and not your hearing for the day?

This time of year with temp and humidity swings our hearing systems can and do change radically from day to day.

Just a thought. Might be worth confirming again in a few days…but yeah, swapping tubes is quick and easy. In my experience, stick with the 12AU7-family for least fuss in the BHK pre.

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Having a spare matched pair for a rainy day is not a bad idea!

The way things have gone in my tube-rolling journey, I have backups for the backups for the backups. :man_facepalming:


Oddly, that happened with me yesterday. It sounded fine at turn on and I let it play to warm up. Later when I went to listen the bass was way down in level. The mid bass and subs have separate amps both fed from the same output of the BHK Pre and both are down in level.

The tubes have 980 hrs on them and have been fine before this. The previous set had about 1500 hrs and were fine when changed, so I will swap them back in. I’ll post the results later.

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Hi psalvet…

I forget if you have a regenerator…if you do a simple solution might
be a) power it off totally…reboot
b) run clean wave

When my system (all ss ) begins to sound thin or off I run clean wave 60 seconds
that usually does the trick.

So if you have regenerator give it a try …might could help…quick cheap and easy…

Best wishes friend

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Curious. Not the symptom I’ve usually associated with long in the tooth tubes. First off, tube degradation is generally gradual, not something that suddenly occurs. I hear the slow degradation as being an increase in noise, sometimes it’s of the ‘corn pop’ variety, a general loss of dynamics because of the raised noise floor. Sudden thinness and brightness - can’t remember ever encountering that and being able to isolate it to tubes. Were I to encounter this I’d first suspect the quality of my mains. Then again, I’ve got the luxury of a box overflowing with new stock and NOS 6922s + 12au7s. So if it persisted for, say, a day I admit I’d be swapping tubes in my BHK pre to find out if that solves the problem.

Well I tried the older tubes (see my post above) and found no difference. However I can adjust levels in the bass crossover and am close to where it was originally.

Before seeing this thread I thought it might be a break in issue with the new PST and I now think it probably is.